A number of motionless mixer types exist, such as Multiflux, helical and others. These mixer types, for the most part, implement a similar general principle to mix fluids together. In these mixers, fluids are mixed together by dividing and recombining the fluids in an overlapping manner. This action is achieved by forcing the fluid over a series of baffles of alternating geometry. Such division and recombination causes the layers of the fluids being mixed to thin and eventually diffuse past one another, eventually resulting in a generally homogenous mixture of the fluids. This mixing process has proven to be very effective, especially with high viscosity fluids.
Static mixers are typically constructed of a series of alternating baffles, of varying geometries, usually consisting of right-handed and left-handed mixing baffles located in a conduit to perform the continuous division and recombination. Such mixers are generally effective in mixing together most of the mass fluid flow, but these mixers are subject to a streaking phenomenon, which has a tendency to leave streaks of completely unmixed fluid in the extruded mixture. The streaking phenomenon often results from streaks of fluid forming along the interior surfaces of the mixer conduit that pass through the mixer essentially unmixed.
There have been attempts made to maintain adequate mixer length while trying to address the streaking phenomenon. For example, the traditional left-handed and right-handed mixing baffles can be combined with baffles causing greater angles of rotation of the flow (180° or 270° baffles) and/or combined with flow inversion baffles, such as the specialized inverter baffles described in U.S. Pat. No. 7,985,020 to Pappalardo and U.S. Pat. No. 6,773,156 to Henning. Each of these latter types of baffles tends to force the fluid from the periphery into the center of the mixing baffles, and vice versa. While such approaches do reduce the size of streaks moving through the static mixer, the mixing is less efficient because the movement of all central flow to the periphery and all peripheral flow to the center requires significant shifting movement of the entire fluid flow moving through these flow inversion baffles, which can in some instances increase the backpressure in the static mixer in a significant manner. Moreover, when the fluid flow includes alternating layers of at least two components, the high amount of flow shifting caused by known flow inversion baffles can lead to layer disruption or jumbling together of the layers in such a manner that may produce additional flow streaks that must later be diffused by other mixing elements in the static mixer, thereby increasing the total length of a mixer.
Therefore, it would be desirable to further enhance the flow shifting or inverting mixing elements used with static mixers of this general type, so that the mixing performance is further optimized at each mixing element and so that the increase in backpressure may be minimized.